Piston for two-stroke internal-combustion engines



Aug. 7, 1945. H. LIEBERHERR 2,381,065

PISTON FOR TWO-STROKE INTERNAL-COMBUSTION ENGINE Filed Aug. 6, 194a ATTO R N EYS INVENTOR W HAM? Z/EBERHEIFIE BY QM Dina 4 ,E

invention.-

. illustrated Patented Aug. -7, 1945 rrs'ron' non 'rwo-s'moxn COMBUSTION ENGINES Hm linemen. Winterthur,

Switzerland, assignor to Sober Ereres, SocleteAnonyme, Winterthur, Swlixerland Application sum s, 194:, Serial No.

"In Switzerland October 24,

2 Claims. 4 (01. 123-55) The invention relates'to a piston for two-stroke internal combustion engines which has a space serving as a storage chamber for compressed gases and lying between the piston rings provided near the working space and the oil scraper ring near the crankcase.

Known proposals for the use of such pistonsprovide an annular space let-into the sliding surface or body of the piston and situated near the crown of the piston, this space being designed as an expansion chamber closed and sealed on both sides by means of packing rings and intended to prevent oil from the'crankcase making its way into the working space when the pressure in the crankcase is higher than that prevailing in the working space. Such pistons are unsuitable for fitting in two-stroke reciprocatingengines because in certain positions of the piston, an undesirable, direct passage of fresh air would take place past the piston itself, from inlet to exhaust, and would thus lead to l es.

The invention is characterisedby the fact that the space-serving as a storage chamber for compressedgases, and whichmay be executed in one or more sections. is situated in the piston. part which lies near .the'oil scraper ring and which *rema outside the region of the inlet and er: lgnust ports during the whole stroke of the'p'ise' The invention is explained more detail below with the aid of thewirawing.

Fig. 1 shows a two-stroke/internal combustion piston designed in accordance with the.

engine invention.

Fig. 2 is the pressure diagram corresponding to this two-stroke engine. 5

The changes in pressure then arising are plotted in curve p (Fig; 2). of oil being drawn i When the piston moves downwards, during the expansion stroke E, the airior combustion gas is not able ring joint, so that the pressure. 1) may sink below the atmospheric pressure A! and below the pres sure P of the crankcase and oil may penetrate into the clearance space and from there into the working space.

To' prevent'the oil losses described, a pace 1 is provided in the sliding surface of piston I between the compression rings and the oil I scraper ring 8, which space serves as a storage space for compressed gases and is designed in the form of a groove runningroundthe piston.' The space or groove I running round the piston must be situated at a point in the sliding surface of .the

piston'- which remains outside the region of the inletand exhaust .ports s during the whole stroke of the piston and which as'a consequence lies near .the oil scraper ring 6.'

Fig. 3 illustrates on a larger scale the cross section through the storage space in'thepiston shown in Fig. -1-.

Fig. i is the side view of another piston; of the, Fig. 5 is a view along lin'e H of Fig. '4. The two-stroke internal combustion engine has a working piston I \which re-[ ciprocates in a cylinder 2. At'the end facing the working space-I of the cylinder. the piston I is into the exhaustipbi'ts and partly compressed.

' pressure? in the crankcase.

F the cylinder which comprises a pi'sbination with It may be expedient to divide the storage space 1 formed by the groove running round the piston intd'two'separate spaces which are placed near the-oil scraperring at points on the sliding surface of ,the' piston which lie on either side of the plane of' oscillation of the connecting-rod. and

.which as aiconsequence are free from, or at any rate onlyzto an-lnsignmcantextent subjected to,

the normal pressure exerted by'the connecting -rod 8. The advantage of this is that those sliding surfaces ofthe piston which have to support the rather high normal pressures are not broken by a groove that'destr'oys the oil film running along the length of the clearance between the sliding surfaces ofcyl inder and piston and which is enclosed between the oil scraper ring and the lowest piston As curve p of Fig.2 shows when the piston isdesigned in accordance with the invention, the

- storage spaces are able to-influence the pressure prevailingin the clearance space between piston and liner, in such a way thatthe pressure never falls below -the atmospheric I-claim: L'Inan internal There is then no danger nto the clearance space and into the adjacent working space.

to now .so quickly through the piston cylinder and thus impairs the lubrication of the piston.

pressure At and the;

I inlet and exhaust ports in the cylinder, the com bination with the cylinder which comprises a 10 piston having an oilscraper ring near the lower portion thereof, two grooves in the exterior wall of the piston and spaced a short distance-above the oil scraper ring, said grooves being located on the sides of the plane of oscillation of the connecting rod and being so located on the piston that the grooves do not reach the said ports during travel of the piston.

HANS LIEBERHERR. 

